Forward osmosis (FO) is being considered as alternative or supplement technology to reverse osmosis (RO) for wastewater recycling due to its lower energy cost and less irreversible fouling than RO. Our previous study showed that the performance of FO in rejecting disinfection byproducts (DBPs), a critical aspect for wastewater recycling, was better than or comparable with that of RO. Because the current FO transport models, many of which were adopted from RO, overestimated DBP transport, it was hypothesized that the reverse salt flux from draw to feed, a phenomenon unique to FO, contributed to the improved DBP rejection. In this study, we tested this hypothesis by evaluating DBP transport through a commercial FO membrane (Aquaporin) under different reverse salt flux. Different concentrations and/or type of draw solute were used, including 0.2, 0.5, and 1 M sodium chloride, 1 M magnesium sulfate, and 1.5 M glucose. A total of sixteen DBPs including nine halogenated DBPs and seven nitrosamines were tested. For halogenated DBPs, DBP permeance was lower at higher reverse salt flux, suggesting retarded forward DBP transport by reverse salt flux. In contrast, nitrosamine permeance was independent of the reverse salt flux. To improve the prediction accuracy of the solution-diffusion model, hinderance factors were developed to represent the retarding effect of reverse salt flux on active layer (Ka) and supporting layer (Kb). The value of Ka was determined by subtracting the free volume occupied by salt in active layer from the total free volume, while Kb was calculated based on the interaction between DBP and the polymeric matrix of the supporting layer. Preliminary results suggest that reverse salt flux exhibited a stronger effect in retarding DBP transport in the supporting layer than in the active layer. After incorporating Ka and Kb, the solution-diffusion model showed improved accuracy in predicting DBP permeance through Aquaporin membrane. Lastly, the effect of reverse salt flux on DBP transport was evaluated on 4 other membranes being tested for FO applications.

Effects of reverse salt flux on the transport of disinfection byproducts in forward osmosis

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.